KR102400346B1 - Conductive carbon, electrode material including said conductive carbon, and electrode using said electrode material - Google Patents

Abstract

The conductive carbon guide|induced to the electrical storage device which has a high energy density is provided.
The conductive carbon of this invention is carbon containing a hydrophilic part, and content of the hydrophilic part is 10 mass % or more of the whole conductive carbon. In the manufacture of the electrode of an electrical storage device, when a rolling process is performed to the active material layer containing the active material particle formed on the electrical power collector, and the conductive carbon of this invention, the conductive carbon of this invention spreads in the form of grass by the pressure, and it densifies, Active material particles approach each other, and the conductive carbon of this invention extrudes and fills in the clearance gap formed between adjacent active material particles. As a result, the amount of active material per unit volume in the electrode obtained after a rolling process increases, and an electrode density rises.

Description

Conductive carbon, the electrode material containing this conductive carbon, and the electrode using this electrode material {CONDUCTIVE CARBON, ELECTRODE MATERIAL INCLUDING SAID CONDUCTIVE CARBON, AND ELECTRODE USING SAID ELECTRODE MATERIAL}

The present invention relates to conductive carbon used in electrical storage devices such as secondary batteries, electric double layer capacitors, redox capacitors, and hybrid capacitors having high energy density. This invention also relates to the electrode material containing the said conductive carbon, and the electrode for electrical storage devices using this electrode material.

Power storage devices such as secondary batteries, electric double-layer capacitors, redox capacitors and hybrid capacitors are used to power information devices such as mobile phones and notebook computers, motor-driven power sources for low-emission vehicles such as electric and hybrid vehicles, and energy regeneration systems. Although the device is widely considered for application for this purpose, in order to satisfy the request|requirement of performance improvement and miniaturization in these electrical storage devices, the improvement of the energy density is desired.

In these electrical storage devices, an electrode active material that exhibits capacity by a Faraday reaction involving electron transfer with ions in an electrolyte (including an electrolyte solution) or a non-Faraday reaction without electron transfer is used for energy storage. And, these active materials are generally used in the form of a composite material with a conductive agent. As a conductive agent, conductive carbons, such as carbon black, natural graphite, artificial graphite, and a carbon nanotube, are normally used. These conductive carbons play a role in imparting conductivity to the composite material when used in combination with an active material with low conductivity, but also act as a matrix to absorb the volume change caused by the reaction of the active material, and even if the active material is mechanically damaged, electrons It also plays a role of securing a conduction path.

By the way, the composite material of these active materials and conductive carbon is generally manufactured by the method of mixing the particle|grains of an active material, and conductive carbon. Since conductive carbon does not fundamentally contribute to the improvement of the energy density of an electrical storage device, in order to obtain the electrical storage device which has a high energy density, it is necessary to reduce the amount of conductive carbon per unit volume and to increase the amount of active materials. Then, by improving the dispersibility of conductive carbon or reducing the structure of conductive carbon, the distance between active material particles is made close, and examination which increases the amount of active material per unit volume is performed.

For example, Patent Document 1 (Japanese Patent Application Laid-Open No. 2004-134304) contains a carbon material with a small particle diameter (acetylene black in the example) having an average primary particle diameter of 10 to 100 nm, and a blackening degree of 1.20 or more. A non-aqueous secondary battery having a positive electrode having The paint used for preparing the positive electrode is a high-speed rotating homogenizer-type disperser, a high-speed rotating homogenizer-type disperser, or a high shear dispersion device such as a planetary mixer having three or more rotating shafts, or It is obtained by adding the dispersion which disperse|distributed the mixture of the said carbon material, binder, and a solvent to the paste which disperse|distributed the mixture of a positive electrode active material, a binder, and a solvent with the strong shear dispersing apparatus, and further disperse|distributes it. By using an apparatus having a strong shear force, the carbon material, which is difficult to be dispersed due to a small particle diameter, is uniformly dispersed.

In addition, Patent Document 2 (Japanese Patent Application Laid-Open No. 2009-35598) discloses a non-aqueous secondary battery comprising acetylene black having a BET specific surface area of 30 to 90 m 2 /g, a DBP absorption amount of 50 to 120 mL/100 g, and a pH of 9 or more. A conductive agent for an electrode is disclosed. The electrode of a secondary battery is comprised by dispersing this mixture of acetylene black and an active material in the liquid containing a binder, preparing a slurry, and apply|coating and drying this slurry on an electrical power collector. Acetylene black having the above characteristics has a lower structure than Ketjen black or conventional acetylene black, so the bulk density of the mixture with the active material is improved, and the battery capacity is improved.

Japanese Patent Laid-Open No. 2004-134304 Japanese Patent Laid-Open No. 2009-35598

Although the further improvement of energy density is always requested|required of an electrical storage device, as a result of the inventors examining, it is difficult to make conductive carbon efficiently enter between active material particles even if it is a method similar to patent document 1 or patent document 2, Therefore, between active material particles It was difficult to increase the amount of active material per unit volume by making the distance closer. Therefore, there existed a limit in the improvement of the energy density by the positive electrode and/or a negative electrode using the composite material of active material particle and conductive carbon.

Then, the objective of this invention is providing the conductive carbon guide|induced to the electrical storage device which has a high energy density.

As a result of the inventors earnestly examining, when the electrode of an electrical storage device was comprised using the composite material of the conductive carbon obtained by giving strong oxidation treatment to a carbon raw material, and active material particle, it discovered that an electrode density rose significantly. And as a result of analyzing this conductive carbon in detail, conductive carbon guide|induced to the electrical storage device which has a high energy density that conductive carbon contains many hydrophilic parts and content of a hydrophilic part is 10 mass % or more of the whole conductive carbon is obtained could see that

Therefore, first, this invention relates to the conductive carbon characterized by the above-mentioned conductive carbon including a hydrophilic part as conductive carbon for the electrode of an electrical storage device, and content of the said hydrophilic part being 10 mass % or more of the whole conductive carbon.

In this invention, the "hydrophilic part" of conductive carbon has the following meanings. That is, 0.1 g of conductive carbon is added to 20 ml of aqueous ammonia solution of pH11, and the liquid obtained by performing ultrasonic irradiation for 1 minute is left to stand for 5 hours, and a solid-phase part is precipitated. The part dispersed in the aqueous ammonia solution of pH 11 without precipitation is the "hydrophilic part". In addition, content with respect to the whole conductive carbon of a hydrophilic part is calculated|required with the following method. After precipitation of the solid portion, the remaining portion from which the supernatant is removed is dried, and the weight of the dried solid is measured. The weight which subtracted the weight of the solid after drying from the weight 0.1g of the first conductive carbon is the weight of the "hydrophilic part" disperse|distributed to the aqueous ammonia solution of pH11. And weight ratio with respect to the weight 0.1g of the first conductive carbon of the weight of a "hydrophilic part" is content of the "hydrophilic part" in conductive carbon.

The ratio of the hydrophilic part in conductive carbons, such as carbon black, natural graphite, and carbon nanotube, used as a conductive agent in the electrode of the conventional electrical storage device is 5 mass % or less of the whole. However, if these raw materials are subjected to oxidation treatment using these materials as raw materials, they are oxidized from the surface of the particles, hydroxy groups, carboxy groups, or ether bonds are introduced into carbon, and conjugated double bonds of carbon are oxidized to form carbon single bonds, partially The carbon-to-carbon bond is cleaved to form a hydrophilic moiety on the particle surface. And when the intensity|strength of an oxidation process is strengthened, the ratio of the hydrophilic part in a carbon particle will increase, a hydrophilic part will occupies 10 mass % or more of the whole conductive carbon, and particle|grains will aggregate through this hydrophilic part.

1 is a diagram schematically illustrating changes in aggregates when pressure is applied to such aggregates. When pressure is applied to the aggregated aggregate through the hydrophilic portion as shown in the upper drawing of FIG. 1, the weak hydrophilic portion cannot withstand the pressure, and the aggregate collapses as illustrated in the central drawing of FIG. In addition, when the pressure is increased, not only the hydrophilic portion of the surface of the carbon particles but also the non-oxidized portion at the center of the particle is deformed or partially insulated, thereby compressing the aggregate as a whole. However, even when compressed, the hydrophilic part of the carbon particle becomes a binder, and as shown in the lower figure of FIG. And the carbon spread in the form of grass is compressed very densely. In addition, the "grass shape" refers to a state in which the grain boundaries of the primary carbon particles are not confirmed in the SEM photograph taken at a magnification of 25000 times, and non-particulate amorphous carbon is connected.

The conductive carbon of this invention is easy to adhere to the surface of an active material particle, and when it receives pressure, it is compressed integrally, and it spreads in the form of a paste, and has the characteristic that it is hard to be scattered. Therefore, when the conductive carbon and active material particles of the present invention are mixed for an electrode of an electrical storage device to obtain an electrode material, in the process of mixing, conductive carbon adheres to the surface of the active material particles and covers the surface, and the dispersibility of the active material particles is improved make it When the pressure applied to conductive carbon at the time of electrode material manufacture is large, at least one part of conductive carbon will spread in the form of grass, and the surface of an active material particle will be covered partially. And when an active material layer is formed using this electrode material on the current collector of the electrode and pressure is added to the active material layer, most or all of the conductive carbon of the present invention spreads in a grass shape as shown in the lower drawing of FIG. By densification while covering the surface of the active material particles, the active material particles approach each other, and accordingly, the conductive carbon of the present invention covers the surface of the active material particle while covering the surface of the active material particle as well as the gap formed between the adjacent active material particles It exists on the surface of the active material particle It is also extruded and densely filled inside the hole (including the gap between the primary particles identified in the secondary particles) to be formed (see Fig. 3). Therefore, the amount of active material per unit volume in an electrode increases, and an electrode density increases. Moreover, while having sufficient electroconductivity to function as a electrically conductive agent, the paste-shaped conductive carbon with which it filled densely does not suppress the impregnation of the electrolyte solution in an electrical storage device. As a result, the improvement of the energy density of an electrical storage device is brought about.

On the other hand, conductive carbon such as carbon black used as a conductive agent in the electrode of a conventional electrical storage device or even oxidized carbon thereof is carbon lacking in oxidation strength, and the content of the hydrophilic portion is less than 10% by mass of the entire conductive carbon. Even if the electrode of an electrical storage device is comprised using a thing, the increase of an electrode density is not enough. Conductive carbon of this invention WHEREIN: Since especially high electrode density is obtained that content of a hydrophilic part is 12 mass % or more and 30 mass % or less of the whole conductive carbon, it is preferable.

The conductive carbon of this invention can be manufactured suitably by oxidation-processing the carbon raw material which has a space|gap. The voids include internal voids of Ketjen black, voids within tubes of carbon nanofibers or carbon nanotubes, and voids between tubes, in addition to voids of the porous carbon powder.

When the electrode of an electrical storage device is comprised using the composite material of the conductive carbon of this invention and electrode active material particle as an electrode material, as mentioned above, the improvement of the energy density of an electrical storage device will be brought about. Therefore, this invention also relates to the electrode material characterized by including the conductive carbon and electrode active material particle of this invention as an electrode material for electrical storage devices.

The electrode material of this invention WHEREIN: It is preferable that the average particle diameter of the said electrode active material particle is 0.01-2 micrometers. Since the conductive carbon of this invention adheres to the surface of an active material particle and covers the surface, even if the average particle diameter of an active material particle is as small as 0.01-2 micrometers, aggregation of an active material particle can be suppressed.

In the electrode material of the present invention, the electrode active material particles are microparticles having an average particle diameter of 0.01 to 2 μm that can operate as a positive electrode active material or a negative electrode active material, and larger than 2 μm that can operate as the same electrode active material as the microparticles 25 It is preferably composed of coarse particles having an average particle diameter of mu m or less. Coarse particles increase the electrode density, thereby improving the energy density of the electrical storage device. In addition, by the pressure applied to the electrode material at the time of electrode manufacturing, the microparticles are extruded and filled into the gaps formed between the adjacent coarse particles together with the conductive carbon while pressing the conductive carbon of the present invention, so that the electrode density is further increased. increase, and the energy density of the power storage device is further improved. In addition, the average particle diameter of active material particle|grains means the 50% diameter (median diameter) in the measurement of the particle size distribution using the light-scattering particle size meter.

The electrode material of this invention WHEREIN: It is preferable that the conductive carbon which has electrical conductivity higher than other conductive carbon, especially the conductive carbon of this invention is further contained. By the pressure applied to the electrode material at the time of electrode manufacture, these carbons are also densely filled in the gaps formed by the active material particles adjacent together with the conductive carbon of the present invention, and the conductivity of the entire electrode is improved, so the energy of the electrical storage device The density is further improved.

As mentioned above, when the electrode of an electrical storage device is comprised using the electrode material containing the conductive carbon and active material particle of this invention, the energy density of an electrical storage device will improve. Accordingly, the present invention also relates to an electrode characterized in that it has an active material layer formed by applying pressure to the electrode material of the present invention as an electrode of an electrical storage device. Moreover, it is thought that it is because most or all of the surface of an active material particle is coat|covered with the conductive carbon of this invention which spread in the form of grass to the inside of the hole which exists in the surface of an active material particle in an electrode, but the electrolyte solution in an electrical storage device It turns out that dissolution of the active material with respect to is suppressed significantly, and cycling characteristics of an electrical storage device improve significantly.

(Effects of the Invention)

The conductive carbon of the present invention tends to adhere to the surface of the active material particles, and when pressure is applied, it is compressed integrally, spreads in a pasty shape, and is difficult to be scattered. Conductive carbon is attached to the surface of the active material particles in the process to cover the surface to improve the dispersibility of the active material particles. Moreover, when a pressure is applied to the electrode material containing active material particle and the conductive carbon of this invention in manufacture of the electrode of an electrical storage device, most or all of the conductive carbon of this invention spreads in the form of grass by the pressure, and the active material particle It is densified while covering the surface, and the active material particles approach each other, and thereby, the conductive carbon of the present invention covers the surface of the active material particle while covering the surface of the active material particle as well as the gap formed between the adjacent active material particles, as well as the pores existing on the surface of the active material particle It is also extruded and densely filled inside. Therefore, the amount of active material per unit volume in an electrode increases, and an electrode density increases. Moreover, while having sufficient electroconductivity to function as a electrically conductive agent, the paste-shaped conductive carbon with which it filled densely does not suppress the impregnation of the electrolyte solution in an electrical storage device. As a result, the improvement of the energy density of an electrical storage device is brought about.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which showed the change of the aggregate when a pressure is applied to the aggregate of the conductive carbon of an Example modelly.
It is a figure which showed the relationship between content of a hydrophilic part, and an electrode density about the conductive carbon of an Example and a comparative example.
3 is a SEM photograph of a cross section of an electrode having an active material layer containing conductive carbon and active material particles of an embodiment, (A) is a photograph at 1500 times, (B) is a photograph at 25000 times.
4 is a SEM photograph of a cross section of an electrode having an active material layer containing conductive carbon and active material particles of a comparative example, (A) is a photograph at 1500 times, (B) is a photograph at 25000 times.
Fig. 5 is a view showing the result of measuring the pore distribution of the electrodes shown in Figs. 3 and 4 by a nitrogen gas adsorption method.
It is a figure which shows the rate characteristic of the lithium ion secondary battery provided with the electrode which has the active material layer containing the conductive carbon of an Example or a comparative example, and active material particle.
7 is a view showing cycle characteristics of the lithium ion secondary battery showing the rate characteristics in FIG. 6 .
It is a figure which shows the rate characteristic of the lithium ion secondary battery provided with the electrode which has the active material layer containing the conductive carbon of an Example or a comparative example and the active material particle of a different kind.
9 is a view showing cycle characteristics of the lithium ion secondary battery showing the rate characteristics in FIG. 8 .
It is a figure which shows the rate characteristic of the lithium ion secondary battery provided with the electrode which has an active material layer containing conductive carbon of an Example or a comparative example, and another type of active material particle.
11 is a view showing cycle characteristics of the lithium ion secondary battery showing the rate characteristics in FIG. 10 .
It is a SEM photograph of 50000 times of the mixture obtained by dry-mixing the conductive carbon of an Example, acetylene black, and the particle|grains of an active material.
It is a figure which shows the rate characteristic of the lithium ion secondary battery provided with the electrode which has an active material layer containing conductive carbon of an Example or a comparative example, and active material particle.
14 is a view showing cycle characteristics of the lithium ion secondary battery having the rate characteristics shown in FIG. 13 .
It is an SEM photograph of the conductive carbon of an Example and a comparative example.
It is a figure which shows the result of having investigated the influence of a press pressure about the conductive carbon of an Example and a comparative example, (A) shows the relationship between a press pressure and a density, (B) shows the relationship between a press pressure and a density increase rate, respectively there is.
It is a figure which shows the result of having investigated the influence of press pressure about the conductive carbon of an Example and a comparative example, (A) shows the relationship between a press pressure and electrical conductivity, (B) shows the relationship between a press pressure and electrical conductivity increase rate, respectively there is.
It is an SEM photograph of 50000 times of the mixture obtained by dry-mixing the conductive carbon or acetylene black of an Example, and the fine particle of an active material.
It is a SEM photograph of 100000 times of the mixture obtained by dry-mixing the conductive carbon or acetylene black of an Example, and the coarse particle of an active material.

The conductive carbon of this invention contains a hydrophilic part, Content of the hydrophilic part is 10 mass % or more of the whole conductive carbon, Preferably they are 12 mass % or more and 30 mass % or less. When oxidation treatment is performed on a carbon raw material, preferably a carbon raw material having voids, it is oxidized from the surface of the particles to introduce a hydroxyl group, a carboxyl group or an ether bond into the carbon, and a conjugated double bond of carbon is also oxidized to form a carbon single bond. , the intercarbon bond is partially cleaved to create a hydrophilic moiety on the particle surface. And when the intensity|strength of an oxidation process is strengthened, the ratio of the hydrophilic part in a carbon particle will increase, and a hydrophilic part will occupy 10 mass % or more of the whole conductive carbon.

Conductive carbon in this way is easy to adhere to the surface of an active material, and when it receives pressure, it compresses integrally, spreads in the form of a paste, and has the characteristic that it is hard to be scattered.

The conductive carbon of this invention,

(a1) a step of treating the carbon raw material having pores with an acid;

(b1) a step of mixing the product after acid treatment with the transition metal compound;

(c1) pulverizing the obtained mixture to generate a mechanochemical reaction;

(d1) a step of heating the product after the mechanochemical reaction in a non-oxidizing atmosphere, and

(e1) step of removing the transition metal compound and/or its reaction product from the product after heating

It can be preferably obtained by the first manufacturing method comprising

In the first production method, carbon having pores such as porous carbon powder, Ketjen black, furnace black having pores, carbon nanofibers and carbon nanotubes is used as a carbon raw material. As the carbon raw material having voids, it is preferable to use carbon having a specific surface area of micropores having a diameter of 2 nm or less measured by the MP method of 200 m 2 /g or more, and carbon having an average primary particle diameter of 200 nm or less. It is preferable to use, and it is also preferable to use carbon having a spherical particle shape. It is easy to modify|denature the carbon raw material of this range into the conductive carbon of this invention with a 1st manufacturing method. Among them, spherical particles such as Ketjen Black and voided furnace black are particularly preferable. Even if it performs the process similar to a 1st manufacturing method using solid carbon as a raw material, it is difficult to obtain the conductive carbon of this invention.

In the step (a1), the carbon raw material is immersed in acid and left to stand. You may irradiate an ultrasonic wave at the time of this immersion. As the acid, an acid commonly used for oxidation treatment of carbon, such as nitric acid, a mixture of nitric acid and sulfuric acid, and an aqueous hypochlorous acid solution can be used. The soaking time depends on the concentration of the acid, the amount of the carbon raw material to be treated, and the like, but is generally in the range of 5 minutes to 5 hours. After the carbon after acid treatment is sufficiently washed with water and dried, it is mixed with a transition metal compound in step (b1).

(b1) Examples of the transition metal compound added to the carbon raw material in the step include inorganic metal salts such as halides, nitrates, sulfates and carbonates of transition metals, formates, acetates, oxalates, methoxides, ethoxides, and isopropoxides. organometallic salts, such as these, or mixtures thereof can be used. These compounds may be used independently and may mix and use 2 or more types. A compound containing other transition metals may be mixed and used in a predetermined amount. In addition, as long as the reaction is not adversely affected, a compound other than the transition metal compound, for example, an alkali metal compound, may be added together. Since the conductive carbon of this invention is mixed with active material particle and used in manufacture of the electrode of an electrical storage device, when the compound of the element which comprises an active material is added to a carbon raw material, mixing of the element which can become an impurity with respect to an active material is prevented It is preferable because it can be done.

In step (c1), the mixture obtained in step (b1) is pulverized to generate a mechanochemical reaction. Examples of the pulverizer for this reaction include a Leica machine, a ball mill, a bead mill, a rod mill, a roller mill, a stirred mill, a planetary mill, a vibrating mill, a hybridizer, a mechanochemical compounding device, and a jet mill. The pulverization time is not strictly limited depending on the pulverizer used or the amount of carbon to be treated, but is generally in the range of 5 minutes to 3 hours. The step (d1) is performed in a non-oxidizing atmosphere such as a nitrogen atmosphere or an argon atmosphere. The heating temperature and heating time are appropriately selected depending on the transition metal compound used. The subsequent (e1) process WHEREIN: After removing by means, such as dissolving a transition metal compound and/or its reaction product with an acid, from the product after heating, the conductive carbon of this invention can be obtained by fully wash|cleaning and drying.

In the first production method, in the step (c1), the transition metal compound acts to accelerate the oxidation of the carbon raw material by a mechanochemical reaction, and the oxidation of the carbon raw material proceeds rapidly. By this oxidation, the conductive carbon containing 10 mass % or more of hydrophilic parts of the whole conductive carbon is obtained.

The conductive carbon of this invention further,

(a2) a step of mixing a carbon raw material having voids and a transition metal compound;

(b2) heating the obtained mixture in an oxidizing atmosphere, and

(c2) a step of removing the transition metal compound and/or its reaction product from the product after heating

It can be preferably obtained also by the second manufacturing method comprising

Also in the second production method, carbon having pores such as porous carbon powder, Ketjen black, furnace black having pores, carbon nanofibers and carbon nanotubes is used as the carbon raw material. As the carbon raw material having voids, it is preferable to use carbon having a specific surface area of micropores having a diameter of 2 nm or less measured by the MP method of 200 m 2 /g or more, and carbon having an average primary particle diameter of 200 nm or less. It is preferable to use, and it is also preferable to use carbon having a spherical particle shape. The carbon raw material of this range is easy to modify|denature into the conductive carbon of this invention with a 2nd manufacturing method. Among them, spherical particles such as Ketjen Black and voided furnace black are particularly preferable. Even if it performs the process similar to a 2nd manufacturing method using solid carbon as a raw material, it is difficult to obtain the conductive carbon of this invention.

As the transition metal compound added to the carbon raw material in the step (a2), inorganic metal salts such as halides, nitrates, sulfates and carbonates of transition metals, formates, acetates, oxalates, methoxides, ethoxides, and isopropoxides organometallic salts, such as these, or mixtures thereof can be used. These compounds may be used independently and may mix and use 2 or more types. You may mix and use the compound containing other metals in predetermined amounts. In addition, as long as the reaction is not adversely affected, a compound other than the transition metal compound, for example, an alkali metal compound, may be added together. Since this conductive carbon is mixed with the active material particles in the manufacture of the electrode of the electrical storage device, if a compound of an element constituting the active material is added to the carbon raw material, mixing of elements that may become impurities into the active material can be prevented. It is preferable because there is

The step (b2) is carried out in an oxygen-containing atmosphere, for example, air, at a temperature at which carbon is partially lost but not completely lost, preferably at a temperature of 200 to 350°C. The subsequent (c2) process WHEREIN: After removing by means, such as dissolving a transition metal compound and/or its reaction product with an acid, from the product after heating, the conductive carbon of this invention can be obtained by fully wash|cleaning and drying.

In the second production method, the transition metal compound acts as a catalyst for oxidizing the carbon raw material in the heating step in an oxidizing atmosphere, so that the carbon raw material is oxidized rapidly. By this oxidation, the conductive carbon containing 10 mass % or more of hydrophilic parts of the whole conductive carbon is obtained.

The conductive carbon of this invention is obtained by giving strong oxidation treatment to a carbon raw material, It is also possible to accelerate|stimulate oxidation of a carbon raw material by methods other than a 1st manufacturing method and a 2nd manufacturing method.

The conductive carbon of this invention is mixed with the particle|grains of the electrode active material which expresses capacity by the Faraday reaction accompanying electron transfer with the ion in the electrolyte of an electrical storage device, or the non-Faraday reaction accompanying electron transfer 2 It is used for the electrode of electrical storage devices, such as a secondary battery, an electric double layer capacitor, a redox capacitor, and a hybrid capacitor. A power storage device contains a pair of electrodes (positive electrode, negative electrode) and an electrolyte disposed therebetween as essential elements. do.

The electrolyte disposed between the positive electrode and the negative electrode in the electrical storage device may be an electrolyte held in a separator, a solid electrolyte, or a gel electrolyte, and an electrolyte used in a conventional electrical storage device can be used without particular limitation. Hereinafter, representative electrolytes are exemplified. For lithium ion secondary batteries, an electrolyte solution in which lithium salts such as LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN(CF ₃ SO2) ₂ are dissolved in a solvent such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, etc. It is used in the state hold|maintained by separators, such as a polyolefin fiber nonwoven fabric and a glass fiber nonwoven fabric. In addition, Li ₅ La ₃ Nb ₂ O ₁₂ , Li _{1 . 5} Al _{0 . 5} Ti _1.5 (PO ₄ ) ₃ , Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₇ P ₃ S _{11 and} other inorganic solid electrolytes, lithium salts and polymer compounds such as polyethylene oxide, polymethacrylate, and polyacrylate An organic solid electrolyte composed of a composite of For the electric double layer capacitor and the redox capacitor, an electrolyte solution obtained by dissolving a quaternary ammonium salt such as (C ₂ H ₅ ) ₄ NBF ₄ in a solvent such as acrylonitrile or propylene carbonate is used. For the hybrid capacitor, an electrolyte in which lithium salt is dissolved in propylene carbonate or the like, or an electrolyte in which quaternary ammonium salt is dissolved in propylene carbonate or the like is used.

The positive electrode or negative electrode of the electrical storage device is generally sufficiently kneaded with the solvent in which the binder is dissolved, as needed, the electrode material containing the conductive carbon of the present invention and the electrode active material particles. An active material layer is formed by apply|coating on the electrical power collector for comprised, and after drying this active material layer as needed, it manufactures by giving a rolling process to an active material layer. When a solid electrolyte or a gel electrolyte is used as an electrolyte between a positive electrode and a negative electrode, a solid electrolyte is added to the electrode material containing the conductive carbon of this invention and electrode active material particle for the purpose of ensuring the ion conduction path in an active material layer. Then, the active material layer is formed using the kneaded product obtained by sufficiently kneading these together with the solvent in which the binder is dissolved as needed.

In the process of manufacturing an electrode material by mixing the conductive carbon of this invention and electrode active material particle, since conductive carbon adheres to the surface of an active material particle and covers the surface, aggregation of an active material particle can be suppressed. When the pressure applied to conductive carbon at the time of electrode material manufacture is large, at least one part of conductive carbon will spread in the form of grass, and the surface of an active material particle will be covered partially. In addition, most or all of the conductive carbon of the present invention spreads in a pasty shape by the pressure applied in the course of the rolling treatment of the active material layer, and densifies while covering the surface of the active material particles, so that the active material particles approach each other, according to the present invention of the conductive carbon is densely filled by extruding not only the gap formed between the adjacent active material particles while covering the surface of the active material particle but also the inside of the hole existing on the surface of the active material particle. Therefore, the amount of active material per unit volume in an electrode increases, and an electrode density increases. Moreover, while having sufficient electroconductivity to function as a electrically conductive agent, the paste-shaped conductive carbon with which it filled densely does not suppress the impregnation of the electrolyte solution in an electrical storage device. As a result, the improvement of the energy density of an electrical storage device is brought about.

As a positive electrode active material and negative electrode active material mixed with the conductive carbon of this invention in manufacture of an electrode material, the electrode active material currently used in the conventional electrical storage device can be used without limitation in particular. A single compound may be sufficient as an active material, and the mixture of 2 or more types of compounds may be sufficient as it.

As an example of the positive electrode active material of the secondary battery, first, layered rock salt type LiMO ₂ , layered Li ₂ MnO ₃ -LiMO ₂ solid solution, and spinel type LiM ₂ O ₄ (wherein M is Mn, Fe, Co, Ni or a combination thereof) meaning) can be included. Specific examples thereof include LiCoO ₂ , LiNiO _{2 ,} LiNi _4/5 Co _1/5 O _{2 , LiNi 1/3} Co _1/3 Mn _1/3 O _{2 , LiNi 1/2 Mn 1/2 O 2 , LiFeO 2 ,} LiMnO ₂ , Li ₂ MnO ₃ -LiCoO ₂ , Li ₂ MnO ₃ -LiNiO ₂ , Li ₂ MnO _{3 -LiNi 1/3} Co _1/3 Mn _1/3 O ₂ , Li ₂ MnO _{3 -LiNi 1/2} Mn _{1 / 2} O _{2 ,} Li ₂ MnO _{3 -LiNi 1/2} Mn _1/2 O _{2 -LiNi 1/3} Co _1/3 Mn _1/3 O _{2 , LiMn 2} O _{4 , LiMn 3/2 Ni 1/2} O ₄ can be mentioned. In addition, sulfur and sulfides such as Li ₂ S, TiS ₂ , MoS ₂ , FeS ₂ , VS ₂ , Cr _1/2 V _1/2 S ₂ , selenides such as NbSe ₃ , _{VSe 2} , NbSe _{3 , Cr 2 O 5} , Cr ₃ O ₈ , VO ₂ , V ₃ O ₈ , V ₂ O ₅ , V ₆ O ₁₃ In addition to oxides, LiNi _{0 . 8} Co _{0 . 15} Al _{0 . 05} O ₂ , LiVOPO ₄ , LiV ₃ O ₅ , LiV ₃ O ₈ , MoV ₂ O ₈ , Li _{2 FeSiO 4} , Li _{2 MnSiO 4} , LiFePO ₄ , LiFe _1/2 Mn _1/2 PO _{4 , LiMnPO 4} , Li and complex oxides such as ₃ V ₂ (PO ₄ ) ₃ .

Examples of the negative electrode active material of the secondary battery include Fe ₂ O ₃ , MnO, MnO ₂ , Mn ₂ O ₃ , Mn ₃ O ₄ , CoO, Co ₃ O ₄ , NiO, Ni ₂ O ₃ , TiO, TiO ₂ , SnO, Oxides such as SnO ₂ , SiO ₂ , RuO ₂ , WO, WO ₂ , ZnO, metals such as Sn, Si, Al, Zn, composite oxides such as LiVO ₂ , Li ₃ VO ₄ , Li ₄ Ti ₅ O ₁₂ , Li _{2 . and} nitrides such as ₆ Co _0.4 N, Ge ₃ N ₄ , Zn ₃ N ₂ , and Cu ₃ N .

Examples of the active material in the polarizable electrode of the electric double layer capacitor include carbon materials having a large specific surface area, such as activated carbon, carbon nanofibers, carbon nanotubes, phenol resin carbide, polyvinylidene chloride carbide, and microcrystalline carbon. In the hybrid capacitor, the positive electrode active material exemplified for the secondary battery can be used for the positive electrode, and in this case, the negative electrode is constituted by a polarizable electrode using activated carbon or the like. In addition, the negative electrode active material exemplified for the secondary battery can be used for the negative electrode, and in this case, the positive electrode is constituted by a polarizable electrode using activated carbon or the like. Metal oxides, such as RuO2, MnO2, NiO, can be illustrated as _a positive electrode active material of a redox capacitor, _and a negative electrode is comprised by active material, such as RuO2 _, and polarizable material, such as activated carbon.

Although there is no limitation in the shape or particle diameter of an active material particle, It is preferable that the average particle diameter of an active material particle is 0.01-2 micrometers. Active material particles having an average particle diameter of 0.01 to 2 μm are easy to aggregate, but in the process of obtaining an electrode material by mixing with the conductive carbon of the present invention, the conductive carbon adheres to the surface of the active material particles and covers the surface, so the average particle diameter of the active material particles is Even if it is small, aggregation of an active material particle can be suppressed and the mixed state of an active material particle and conductive carbon can be made uniform. In addition, it is preferable that the average particle diameter of the active material particles is greater than 2 μm and not more than 25 μm. The active material particle which has such a comparatively large particle diameter improves an electrode density by itself, and also accelerates|stimulates the paste-forming of conductive carbon by the pressing force in the process of mixing in electrode material manufacture. In addition, in the process of applying pressure to the active material layer on the current collector in electrode manufacturing, the active material particles having such a relatively large particle size further press the conductive carbon in which at least a part is formed in a grass shape to further spread the conductive carbon in a grass shape. densify. As a result, the electrode density further increases, and the energy density of the power storage device is further improved.

In addition, it is preferable that the active material particles are composed of fine particles having an average particle diameter of 0.01 to 2 μm, and coarse particles having an average particle diameter of 25 μm or larger than 2 μm that can operate as the same polar active material as the micro particles. . In the process of manufacturing the electrode material, since the conductive carbon of the present invention adheres to and covers the surface of coarse particles as well as the surface of fine particles, aggregation of active material particles can be suppressed and the mixed state of active material particles and conductive carbon can be uniformed. can Moreover, as mentioned above, a coarse particle accelerates|stimulates the paste-formation and densification of the conductive carbon of this invention, makes an electrode density increase, and improves the energy density of an electrical storage device. In addition, between the coarse particles adjacent to the conductive carbon spread in a pasty shape, while the fine particles press the conductive carbon of the present invention by the pressure applied to the active material layer formed on the current collector by the rolling process in electrode manufacture. Since the formed gap portion is extruded and filled, the electrode density further increases and the energy density of the electrical storage device is further improved.

Moreover, the conductive carbon of this invention is carbon black, such as Ketjen black, acetylene black, furnace black, and channel black, fullerene, carbon nanotube, carbon nanofiber, graphene, amorphous carbon used for the electrode of the conventional electrical storage device, You may use together with conductive carbon other than the conductive carbon of this invention, such as carbon fiber, natural graphite, artificial graphite, graphitization Ketjen black, mesoporous carbon, and a vapor-process carbon fiber. In particular, it is preferable to use together with carbon which has electrical conductivity higher than the electrical conductivity of the conductive carbon of this invention. Since the conductive carbon of this invention adheres not only to the surface of an active material particle but also to the surface of the conductive carbon used together, and covers the surface, aggregation of the conductive carbon used together can be suppressed. Moreover, by the pressure applied to the active material layer formed on the electrical power collector by the rolling process in electrode manufacture, the conductive carbon used together is a gap part formed by the particle|grains adjacent with the conductive carbon of this invention which spread in the form of grass. Since it is densely charged to the electrode and the conductivity of the entire electrode is improved, the energy density of the power storage device is further improved.

There is no limitation in particular in the mixing method of these active material particles, the conductive carbon of this invention, and the other conductive carbon used together as needed, Although a well-known mixing method can be used, It is preferable to mix by dry mixing, and for dry mixing A Leica machine, a ball mill, a bead mill, a rod mill, a roller mill, a stirring mill, a planetary mill, a vibrating mill, a hybridizer, a mechanochemical compounding apparatus and a jet mill can be used. In particular, when a mechanochemical process is performed to active material particle and the conductive carbon of this invention, since the coating property of the active material particle by the conductive carbon of this invention and the uniformity of coating|cover will improve, it is preferable. In order that the active material particle and the conductive carbon of this invention or the conductive carbon of this invention, and the sum total of another conductive carbon used together as needed may obtain the electrical storage device which has a high energy density, it is 90:10-99.5:0.5 by mass ratio It is preferable that it is the range of, and it is more preferable that it is the range of 95:5 - 99:1. When the ratio of conductive carbon is less than the above-mentioned range, the electroconductivity of an active material layer runs short, and there exists a tendency for the coverage of the active material particle by conductive carbon to fall. Moreover, when there are more ratios of conductive carbon than the above-mentioned range, an electrode density will fall and there exists a tendency for the energy density of an electrical storage device to fall.

As an electrical power collector for the electrode of an electrical storage device, electrically-conductive materials, such as platinum, gold|metal|money, nickel, aluminum, titanium, steel, and carbon, can be used. As the shape of the current collector, any shape such as a film shape, a foil shape, a plate shape, a network shape, an expanded metal shape, and a cylindrical shape can be adopted.

As the binder mixed with the electrode material, known binders such as polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, polyvinyl fluoride, and carboxymethyl cellulose are used. It is preferable that content of a binder is 1-30 mass % with respect to the total amount of mixed material. When it is 1 mass % or less, the intensity|strength of an active material layer is not enough, and when it is 30 mass % or more, problems, such as the discharge capacity of an electrode falling and internal resistance becoming excessive, arise. As the solvent to be mixed with the electrode material, a solvent that does not adversely affect the electrode material, such as N-methylpyrrolidone, can be used without particular limitation.

In the electrode which has the active material layer containing the conductive carbon of this invention, when the pore distribution of an active material layer is measured by the nitrogen gas adsorption method, it turns out that an active material layer has a 5-40 nm diameter pore. Although it is thought that this micropore is a pore in the densified grass-like conductive carbon, it is a magnitude|size sufficient for the electrolyte solution in an electrical storage device to pass through grass-like conductive carbon to reach an active material particle. Therefore, the grass-like conductive carbon in an active material layer does not suppress the impregnation of the electrolyte solution in an electrical storage device. Moreover, it turns out that the densified grass-like conductive carbon exists also inside the hole which exists in the gap part formed between the width|variety of 50 nm or less, adjacent electrode active material particle, and/or the surface of electrode active material particle. Therefore, the electroconductivity of the whole active material layer improves, and an electrode density improves. Conductive carbon, such as carbon black, natural graphite, and carbon nanotube, which is used as a conductive agent in the electrode of the conventional electrical storage device, hardly penetrates into the inside of such narrow gap|interval or a hole. In addition, the "width of the gap formed between the electrode active material particles" means the shortest distance among the distances between adjacent active material particles, and "the width of the hole existing on the surface of the electrode active material particle" means the gap between the opposing points of the opening of the hole. It means the shortest distance among the distances.

In the electrode which has an active material layer containing the conductive carbon of this invention, most or all of the active material particle surfaces in an active material layer are dense, and the conductive carbon of this invention spread to the inside of the hole which exists in the surface of an active material particle in a paste shape. 80% or more of the surface (outer surface) of the active material particles, preferably 90% or more, particularly preferably 95% or more, is in contact with the densified pasty conductive carbon. Although it is thought that this is for this reason, when an electrical storage device is comprised using this electrode, the melt|dissolution of the active material with respect to the electrolyte solution in an electrical storage device is suppressed significantly. Compared with the case where the electrode is composed of active material particles and a conductive agent such as acetylene black in the related art, the dissolved amount of the active material is reduced by about 40% or more. And it originates in the dissolution of an active material being suppressed significantly, and cycling characteristics of an electrical storage device improve significantly. In addition, the coverage of the active material particle surface by grass-shaped conductive carbon is the value computed from the SEM photograph which image|photographed the cross section of the active material layer at 25000 times magnification.

Example

The present invention will be described using the following examples, but the present invention is not limited to the following examples.

(1) Evaluation of 1st manufacturing method, content of hydrophilic part, and electrode density

Example 1

Ketjen Black (trade name EC300J, manufactured by Ketjen Black International, Inc., average primary particle diameter; 40 nm, specific surface area of micropores having a diameter of 2 nm or less obtained from the measurement result of the MP method using nitrogen adsorption; 430 in 300 mL of 60% nitric acid; m 2 g ^-1 ) 10 g was added, and the obtained solution was irradiated with ultrasonic waves for 10 minutes, and then filtered to recover Ketjen Black. The recovered Ketjen Black was washed with water 3 times and dried to obtain acid-treated Ketjen Black. 0.5 g of acid-treated Ketjen Black, 1.98 g of Fe(CH ₃ COO) ₂ , 0.77 g of Li(CH ₃ COO), 1.10 g of C ₆ H ₈ O ₇ .H ₂ O, 1.32 g of CH ₃ COOH, and , H ₃ PO ₄ 1.31 g and 120 mL of distilled water were mixed, and the resulting mixture was stirred with a stirrer for 1 hour, and then evaporated to dryness at 100° C. in the air to collect the mixture. Next, the obtained mixture was introduced into a vibrating ball mill apparatus, and pulverization was performed at 20 hz for 10 minutes. The pulverized powder was heated at 700° C. in nitrogen for 3 minutes to obtain a composite in which LiFePO ₄ was supported on Ketjen Black.

1 g of the obtained composite was added to 100 mL of an aqueous hydrochloric acid solution having a concentration of 30%, and the obtained solution was irradiated with ultrasonic waves for 15 minutes to dissolve LiFePO ₄ in the composite, and the remaining solid was filtered, washed with water, and dried. A part of the dried solid was heated to 900°C in air by TG analysis, and the weight loss was measured. The process of dissolving LiFePO ₄ with an aqueous hydrochloric acid solution, filtration, washing with water and drying is repeated until it can be confirmed that the weight loss is 100%, that is, LiFePO ₄ does not remain, to obtain LiFePO ₄ free conductive carbon .

Then, 0.1 g of the obtained conductive carbon was added to 20 ml of aqueous ammonia solution of pH11, and ultrasonic irradiation for 1 minute was performed. The obtained liquid was left to stand for 5 hours to precipitate a solid part. After precipitation of the solid part, the residual part from which the supernatant liquid was removed was dried, and the weight of the solid after drying was measured. Weight ratio with respect to the weight 0.1g of the first conductive carbon of the weight which subtracted the weight of the solid after drying from the weight 0.1g of the first conductive carbon was made into content of the "hydrophilic part" in conductive carbon.

Fe(CH ₃ COO) ₂ , Li(CH ₃ COO), C ₆ H ₈ O ₇ ·H ₂ O, CH ₃ COOH, and H ₃ PO ₄ A mixture obtained by introducing distilled water into distilled water was 1 After stirring for an hour, it was evaporated to dryness at 100°C in air, and then heated at 700°C in nitrogen for 3 minutes to obtain fine particles of LiFePO ₄ having a primary particle size of 100 nm (average particle size of 100 nm). Next, commercially available coarse particles of LiFePO ₄ (primary particle diameter of 0.5 to 1 μm, secondary particle diameter of 2 to 3 μm, average particle diameter of 2.5 μm), the obtained fine particles, and the conductive carbon were mixed in a ratio of 90:9:1 The electrode material is obtained by mixing in a mass ratio, and 5% by mass of polyvinylidene fluoride and an appropriate amount of N-methylpyrrolidone are added and kneaded sufficiently to form a slurry, and this slurry is coated on an aluminum foil and dried Then, a rolling process was performed and the electrode was obtained. The electrode density was computed from the measured value of the volume and weight of the active material layer on the aluminum foil in this electrode.

Example 2

In the procedure in Example 1, 0.5 g of acid-treated Ketjen Black, 1.98 g of Fe(CH ₃ COO) ₂ , 0.77 g of Li(CH ₃ COO), and 1.10 g of C ₆ H ₈ O ₇ ·H ₂ O and, CH ₃ COOH 1.32 g, H ₃ PO ₄ 1.31 g, and distilled water 120 mL of acid-treated Ketjen Black 1.8 g, Fe(CH ₃ COO) ₂ 0.5 g, Li(CH ₃ COO) 0.19 g, C ₆ H ₈ O ₇ ·H ₂ O 0.28 g, CH ₃ COOH 0.33 g, H ₃ PO ₄ 0.33 g, and distilled water 250 mL Except for changing the order of mixing 250 mL of Example 1 The sequence was repeated.

Example 3

After adding 10 g of Ketjen Black used in Example 1 to 300 mL of 40% nitric acid, and irradiating ultrasonic waves for 10 minutes to the obtained liquid, it filtered and collect|recovered Ketjen Black. The recovered Ketjen Black was washed with water 3 times and dried to obtain acid-treated Ketjen Black. The procedure of Example 2 was repeated except that 1.8 g of this acid-treated Ketjen Black was used instead of 1.8 g of the acid-treated Ketjen Black used in Example 2.

Comparative Example 1

After adding 10 g of Ketjen Black used in Example 1 to 300 mL of 60% nitric acid, and irradiating an ultrasonic wave to the obtained liquid for 1 hour, it filtered and collect|recovered Ketjen Black. The recovered Ketjen Black was washed with water 3 times and dried to obtain acid-treated Ketjen Black. This acid-treated Ketjen Black was heated at 700° C. in nitrogen for 3 minutes. About the obtained conductive carbon, content of the hydrophilic part was measured in the same procedure as the procedure in Example 1. Moreover, the LiFePO4 containing electrode was created by the procedure similar to the procedure in Example ₁ using the obtained conductive carbon, and the electrode density was computed.

Comparative Example 2

After adding 10 g of Ketjen Black used in Example 1 to 300 mL of 30% nitric acid, and irradiating an ultrasonic wave to the obtained liquid for 10 minutes, it filtered and collect|recovered Ketjen Black. The recovered Ketjen Black was washed with water 3 times and dried to obtain acid-treated Ketjen Black. Then, it heated at 700 degreeC in nitrogen for 3 minutes without performing grinding|pulverization by a vibrating ball mill. About the obtained conductive carbon, content of the hydrophilic part was measured in the same procedure as the procedure in Example 1. Moreover, the LiFePO4 containing electrode was created by the procedure similar to the procedure in Example ₁ using the obtained conductive carbon, and the electrode density was computed.

Comparative Example 3

In order to confirm the contribution of the hydrophilic portion to the electrode density, 40 mg of the conductive carbon of Example 1 is added to 40 mL of pure water, ultrasonically irradiated for 30 minutes to disperse the carbon in pure water, and the dispersion is left for 30 minutes to remove the supernatant. , to obtain a solid by drying the remaining portion. About this solid, content of the hydrophilic part was measured in the same procedure as the procedure in Example 1. Moreover, the LiFePO4 containing electrode was created by the procedure similar to the procedure in Example ₁ using the obtained conductive carbon, and the electrode density was computed.

Comparative Example 4

About the Ketjen black raw material used in Example 1, content of the hydrophilic part was measured in the same procedure as the procedure in Example 1. Moreover, the LiFePO4 containing electrode was created by the procedure similar to the procedure in Example ₁ using this conductive carbon, and the electrode density was computed.

It is a figure which showed the relationship between hydrophilic partial content with respect to the conductive carbon of Examples 1-3 and Comparative Examples 1-4, and the electrode density with respect to the electrode of Examples 1-3 and Comparative Examples 1-4. As is clear from FIG. 2, when content of a hydrophilic part exceeds 8 mass % of the whole conductive carbon, an electrode density begins to increase, and when it exceeds 9 mass %, an electrode density begins to increase rapidly, content of a hydrophilic part When 10 mass % of this whole conductive carbon was exceeded, it turned out that the high electrode density of 2.6 g/cc or more is obtained. Moreover, it turned out that the contribution of the hydrophilic part of conductive carbon is large to the improvement of an electrode density evidently from the comparison of the result of Example 1 and the result of the comparative example 3.

(2) Evaluation of the 2nd manufacturing method, content of hydrophilic part, and electrode density

Example 4

Ketjen Black (trade name EC300J, manufactured by Ketjen Black International Co., Ltd., average primary particle diameter; 40 nm, specific surface area of micropores; 430 m 2 g ^-1 ) 0.45 g and Co(CH ₃ COO) ₂ 4H ₂ O 4.98 g And, LiOH·H ₂ O 1.6 g, and distilled water 120 mL were mixed, and the resulting mixture was stirred with a stirrer for 1 hour, and then the mixture was collected by filtration. Then, 1.5 g of LiOH·H ₂ O was mixed using an evaporator, and then heated at 250° C. in air for 30 minutes to obtain a composite in which a lithium cobalt compound was supported on Ketjen Black. Lithium in the complex was added to 100 mL of an aqueous solution obtained by mixing 98% concentrated sulfuric acid, 70% concentrated nitric acid, and 30% hydrochloric acid in a volume ratio of 1:1:1, and the obtained solution was irradiated with ultrasonic waves for 15 minutes. The cobalt compound was dissolved, and the remaining solid was filtered, washed with water, and dried. A part of the dried solid was heated to 900°C in air by TG analysis, and the weight loss was measured. The lithium cobalt compound-free conductivity of the lithium cobalt compound free by repeating the steps of dissolving the lithium cobalt compound with an aqueous hydrochloric acid solution, filtration, washing with water, and drying the above-mentioned process until the weight loss is 100%, that is, it can be confirmed that no lithium cobalt compound remains. got carbon.

Next, about the obtained conductive carbon, content of the hydrophilic part was measured in the same procedure as the procedure in Example 1. Content of the hydrophilic part was 14.5 mass % of the whole carbon.

Li ₂ CO ₃ , Co(CH ₃ COO) ₂ , and C ₆ H ₈ 0 ₇ ·H ₂ O were introduced into distilled water, and the resulting mixture was stirred with a stirrer for 1 hour, and then evaporated to dryness at 100° C. in air. After heating, LiCoO ₂ microparticles having an average particle diameter of 0.5 µm were obtained by heating at 800°C in air for 10 minutes. Next, commercially available coarse particles of LiCoO ₂ (average particle size of 10 µm), the obtained fine particles, and the conductive carbon are mixed in a mass ratio of 90:9:1, and an appropriate amount with 5% by mass of polyvinylidene fluoride in total. of N-methylpyrrolidone was added and kneaded sufficiently to form a slurry, and the slurry was applied on an aluminum foil and dried, followed by a rolling treatment to obtain an electrode. The electrode density was computed from the measured value of the volume and weight of the active material layer on the aluminum foil in this electrode. The value of the electrode density was 4.2 g/cc.

Comparative Example 5

About the Ketjen black raw material used in Example 4, content of the hydrophilic part was measured in the same procedure as the procedure in Example 1. Content of the hydrophilic part was 5 mass % of the whole carbon. Moreover, the LiCoO ₂ containing electrode was created in the same procedure as Example 4, and the electrode density was computed. The value of the electrode density was 3.6 g/cc.

From the comparison of Example 4 and the comparative example 5, it turns out that an electrode density improves significantly as content of a hydrophilic part is 10 mass % or more of the whole conductive carbon.

(3) Evaluation as a lithium ion secondary battery

(i) Active material: LiNi _{0 . 5} Mn _{0 . 3} Co _{0 . 2} O ₂

Example 5

Li ₂ CO ₃ , Ni(CH ₃ COO) ₂ , Mn(CH ₃ COO) ₂ , and Co(CH ₃ COO) ₂ were introduced into distilled water, and the resulting mixture was stirred with a stirrer for 1 hour, and then air LiNi _0.5 Mn _0.3 Co _0.2 O ₂ microparticles having an average particle diameter of 0.5 µm were obtained by evaporation and drying at 100°C, mixing with a ball mill, and heating at 800°C in air for 10 minutes. This microparticle and the conductive carbon of Example 1 were mixed by mass ratio of 90:10, and the preliminary|backup mixture was obtained. Next, 86 parts by mass of commercially available LiNi _0.5 Mn _0.3 Co _0.2 O ₂ coarse particles (average particle diameter of 5 µm), 9 parts by mass of the above-mentioned preliminary mixture, and 2 parts by mass of acetylene black (primary particle diameter; 40 nm, micropores) of 0 m 2 g ^{- 1} ) are mixed, and 3 parts by mass of polyvinylidene fluoride and an appropriate amount of N-methylpyrrolidone are added and sufficiently kneaded to form a slurry, and this slurry is applied on an aluminum foil. And after drying, the rolling process was performed and the positive electrode for lithium ion secondary batteries was obtained. The electrode density was computed from the measured value of the volume and weight of the active material layer on the aluminum foil in this positive electrode. The value of the electrode density was 4.00 g/cc. Moreover, using the obtained positive electrode, the ethylene carbonate/diethyl carbonate 1: ₁ solution of 1M LiPF6 was used as electrolyte solution, and the lithium ion secondary battery which used lithium as the counter electrode was created. About the obtained battery, the charging/discharging characteristic was evaluated under the conditions of a wide range of current densities.

Example 6

94 parts by mass of commercially available LiNi _{0 . 5} Mn _{0 . 3} Co _{0 . 2} O ₂ particles (average particle size: 5 µm), 2 parts by mass of the conductive carbon of Example 1, and 2 parts by mass of acetylene black (primary particle size; 40 nm, specific surface area of micropores; 0 m 2 g ^{- 1} ) After mixing, 2 parts by mass of polyvinylidene fluoride and an appropriate amount of N-methylpyrrolidone are added, and the mixture is sufficiently kneaded to form a slurry. This slurry is coated on aluminum foil and dried, followed by rolling treatment to perform lithium ion A positive electrode for a secondary battery was obtained. The electrode density was computed from the measured value of the volume and weight of the active material layer on the aluminum foil in this positive electrode. The value of the electrode density was 3.81 g/cc. Moreover, using the obtained positive electrode, the ethylene carbonate/diethyl carbonate 1: ₁ solution of 1M LiPF6 was used as electrolyte solution, and the lithium ion secondary battery which used lithium as the counter electrode was created. About the obtained battery, the charging/discharging characteristic was evaluated under the conditions of a wide range of current densities.

Comparative Example 6

94 parts by mass of commercially available LiNi _{0 . 5} Mn _{0 . 3} Co _{0 . 2} O ₂ particles (average particle size: 5 µm) and 4 parts by mass of acetylene black (primary particle diameter; 40 nm, specific surface area of micropores; 0 m 2 g ^{- 1} ) are mixed, and further 2 parts by mass of polyvinylidene fluoride and an appropriate amount of N-methylpyrrolidone, sufficiently kneaded to form a slurry, and the slurry was coated on an aluminum foil and dried, followed by rolling to obtain a positive electrode for a lithium ion secondary battery. The electrode density was computed from the measured value of the volume and weight of the active material layer on the aluminum foil in this positive electrode. The value of the electrode density was 3.40 g/cc. Moreover, using the obtained positive electrode, the ethylene carbonate/diethyl carbonate 1: ₁ solution of 1M LiPF6 was used as electrolyte solution, and the lithium ion secondary battery which used lithium as the counter electrode was created. About the obtained battery, the charging/discharging characteristic was evaluated under the conditions of a wide range of current densities.

3 is a SEM photograph of the cross section of the positive electrode of the lithium ion secondary battery of Example 6, and FIG. 4 is a SEM photograph of the cross section of the positive electrode of the lithium ion secondary battery of Comparative Example 6. In each figure, (A) is a photograph of 1500 magnification, (B) is a photograph of 25000 magnification. Although the thickness of the active material layer is indicated by t in FIGS. 3A and 4A , the lithium ion 2 of Example 6 is the same as the content of the active material particles and carbon in the active material layer. It turns out that the active material layer in a secondary battery is thinner than the active material layer in the lithium ion secondary battery of Comparative Example 6. In addition, from the comparison of Fig. 3 (A) and Fig. 4 (A), in the active material layer in the lithium ion secondary battery of Example 6, the active material particles approach each other to the area of the entire active material layer in the image. It can be seen that the ratio of the area occupied by carbon to the carbon is small. Moreover, as can be grasped|ascertained from FIG.3(B) and FIG.4(B), the form of carbon in both is remarkably different. In the active material layer in the lithium ion secondary battery of Comparative Example 6 (Fig. 4(B)), the grain boundaries of the primary carbon (acetylene black) particles are clear, and in addition to the voids between the carbon particles, the interface between the active material particles and the carbon particles While large voids exist in the vicinity, particularly in the vicinity of pores formed on the surface of the active material particles, in the active material layer in the lithium ion secondary battery of Example 6 (Fig. 3(B)), the grain boundaries of the carbon primary particles are It was not confirmed, and it was found that the carbon was in the form of grass, and that the carbon in the form of grass had penetrated to the deep part of the pores (gaps between primary particles) having a width of 50 nm or less of the particles of the active material, so that there were almost no voids. there is. Moreover, it turns out that 90% or more of the active material particle surfaces are in contact with grass-like carbon. It turned out that the difference in the electrode density in the positive electrode of the lithium ion secondary battery of Example 6 and Comparative Example 6 was caused by the difference in the form of this carbon.

As described above, since the active material layer in Example 6 is thinner than the active material layer in Comparative Example 6, it can be seen that the material filling rate in the active material layer of Example 6 is large, but using the following formula The material filling rate was checked. In addition, a theoretical electrode density is an electrode density when it is assumed that the space|gap in an active material layer is 0 %.

Material filling factor (%) = electrode density × 100/theoretical electrode density (I)

Theoretical electrode density (g/cc)

= 100/{a/X+b/Y+(100-a-b)/Z} (II)

a: mass % of active material with respect to the entire active material layer

b: mass % of carbon with respect to the entire active material layer

100-a-b: mass % of polyvinylidene fluoride with respect to the entire active material layer

X: True density of active material Y: True density of carbon black

Z: true density of polyvinylidene fluoride

As a result, the material filling rate of the active material layer in Example 6 is 86.8%, the material filling rate of the active material layer in the comparative example 6 is 79.1 %, In the electrode containing the conductive carbon of this invention, 7.7% of the filling rate An improvement was confirmed.

About the active material layer in Example 6 and the active material layer in Comparative Example 6 in FIG. 5, the result of having measured the pore distribution by the nitrogen gas adsorption method is shown. It turns out that the active material layer in Comparative Example 6 hardly had pores with a diameter of less than 20 nm, and most of the pores were pores showing a peak at about 30 nm in diameter, about 40 nm in diameter, and about 150 nm in diameter. The pores exhibiting a peak at about 150 nm in diameter are mainly due to the active material particles, and the pores showing peaks at about 30 nm in diameter and about 40 nm in diameter are considered to be pores mainly found between particles of acetylene black. On the other hand, in the active material layer in Example 6, the number of pores with a diameter of about 100 nm or more among the pores of the active material layer in Comparative Example 6 is decreasing, and instead of this, pores in the range of 5 to 40 nm in diameter are increasing. it can be seen that It is thought that the pore of about 100 nm or more in diameter is decreasing because the pore of an active material particle is covered with pasty conductive carbon. Moreover, although it is thought that the pore with a diameter of 5-40 nm is mainly the pore in the densified grass-like conductive carbon, it is a sufficient size for the electrolyte solution in an electrical storage device to pass through the grass-like conductive carbon to reach an active material particle. Therefore, it was judged that the paste-shaped conductive carbon in an electrode did not suppress the impregnation of the electrolyte solution in an electrical storage device.

6 is a diagram showing the relationship between the rate and the discharge capacity per volume of the positive electrode active material layer for the lithium ion secondary batteries of Examples 5, 6, and Comparative Example 6; The lithium ion secondary battery of Example 6 exhibits an increased capacity than the lithium ion secondary battery of Comparative Example 6, and the lithium ion secondary battery of Example 5 has a further increased capacity than the lithium ion secondary battery of Example 6 showed That is, as the electrode density of the positive electrode increased, the discharge capacity per volume also increased. In addition, these secondary batteries exhibited approximately the same rate characteristics. From this, while having sufficient electroconductivity for the grass-shaped conductive carbon contained in the active material layer in the secondary battery of Examples 5 and 6 to function as a conductive agent, impregnation of the electrolyte solution in a secondary battery is carried out It can be seen that it is not suppressed. Although the positive electrode of the secondary battery of Example 5 and the positive electrode of the secondary battery of Example 6 have approximately the same content of active material particles and carbon in the active material layer, the positive electrode of the secondary battery of Example 5 is the positive electrode of Example 6 shows an electrode density higher than that of the positive electrode of the secondary battery of It was thought that this was because it was extruded and filled in the clearance gap formed between particle|grains.

For the lithium ion secondary batteries of Example 6 and Comparative Example 6, charging and discharging were repeated in the range of 4.6 to 3.0 V under conditions of a charge/discharge rate of 60° C. and 0.5 C. 7 shows the results of the obtained cycle characteristics. It can be seen that the secondary battery of Example 6 has superior cycle characteristics than the secondary battery of Comparative Example 6. As can be seen from the comparison of Figs. 3 and 4, substantially the entire surface of the active material particles in the active material layer in the secondary battery of Example 6 is made of grass-like carbon up to the depth of pores on the surface of the active material particles. It was coat|covered, and it was thought that this grass-like carbon was because the deterioration of an active material was suppressed.

(ii) Active material: LiCoO ₂

Example 7

Li ₂ CO ₃ , Co(CH ₃ COO) ₂ , and C ₆ H ₈ 0 ₇ ·H ₂ O were introduced into distilled water, and the resulting mixture was stirred with a stirrer for 1 hour, and then evaporated to dryness at 100° C. in air. After heating, LiCoO ₂ microparticles having an average particle diameter of 0.5 µm were obtained by heating at 800°C in air for 10 minutes. This microparticle and the conductive carbon of Example 1 were mixed by mass ratio of 90:10, and the preliminary|backup mixture was obtained. Next, 86 parts by mass of commercially available coarse particles of LiCoO ₂ (average particle diameter of 10 µm), 9 parts by mass of the above-mentioned preliminary mixture, and 2 parts by mass of acetylene black (primary particle diameter; 40 nm, specific surface area of micropores; 0 m 2 ) g ^{- 1} ) is mixed, and 3 parts by mass of polyvinylidene fluoride and an appropriate amount of N-methylpyrrolidone are added and sufficiently kneaded to form a slurry, and this slurry is coated on an aluminum foil and dried, followed by rolling treatment to obtain a positive electrode for a lithium ion secondary battery. The electrode density was computed from the measured value of the volume and weight of the active material layer on the aluminum foil in this positive electrode. The value of the electrode density was 4.25 g/cc. Moreover, using the obtained positive electrode, the ethylene carbonate/diethyl carbonate 1: ₁ solution of 1M LiPF6 was used as electrolyte solution, and the lithium ion secondary battery which used lithium as the counter electrode was created. About the obtained battery, the charging/discharging characteristic was evaluated under the conditions of a wide range of current densities.

Example 8

94 parts by mass of commercially available LiCoO ₂ particles (average particle size of 10 µm), 2 parts by mass of the conductive carbon of Example 1, and 2 parts by mass of acetylene black (primary particle diameter; 40 nm, specific surface area of micropores; 0 m 2 g ^{- 1} ) is mixed, and 2 parts by mass of polyvinylidene fluoride and an appropriate amount of N-methylpyrrolidone are added and thoroughly kneaded to form a slurry, and this slurry is coated on aluminum foil and dried, followed by rolling treatment. It carried out and obtained the positive electrode for lithium ion secondary batteries. The electrode density was computed from the measured value of the volume and weight of the active material layer on the aluminum foil in this positive electrode. The value of the electrode density was 4.05 g/cc. Moreover, using the obtained positive electrode, the ethylene carbonate/diethyl carbonate 1: ₁ solution of 1M LiPF6 was used as electrolyte solution, and the lithium ion secondary battery which used lithium as the counter electrode was created. About the obtained battery, the charging/discharging characteristic was evaluated under the conditions of a wide range of current densities.

Comparative Example 7

94 parts by mass of commercially available LiCoO ₂ particles (average particle size of 10 µm) and 4 parts by mass of acetylene black (primary particle diameter; 40 nm, specific surface area of micropores; 0 m 2 g ^{- 1} ) are mixed, and 2 parts by mass Polyvinylidene fluoride and an appropriate amount of N-methylpyrrolidone were added, kneaded sufficiently to form a slurry, and the slurry was coated on an aluminum foil and dried, followed by rolling to obtain a positive electrode for a lithium ion secondary battery. . The electrode density was computed from the measured value of the volume and weight of the active material layer on the aluminum foil in this positive electrode. The value of the electrode density was 3.60 g/cc. Moreover, using the obtained positive electrode, the ethylene carbonate/diethyl carbonate 1: ₁ solution of 1M LiPF6 was used as electrolyte solution, and the lithium ion secondary battery which used lithium as the counter electrode was created. About the obtained battery, the charging/discharging characteristic was evaluated under the conditions of a wide range of current densities.

About the active material layer in Example 8 and the active material layer in Comparative Example 7, the material filling rate was confirmed using the formulas (I) and (II) mentioned above. As a result, the material filling rate of the active material layer in Example 8 is 85.6 %, the material filling rate of the active material layer in Comparative Example 7 is 79.1 %, In the electrode containing the conductive carbon of this invention, 6.5% of the filling rate An improvement was confirmed.

FIG. 8 is a diagram showing the relationship between the rate and the discharge capacity per volume of the positive electrode active material layer for the lithium ion secondary batteries of Examples 7, 8, and Comparative Example 7. FIG. It turns out that the discharge capacity also increases as the electrode density increases similarly to the result shown in FIG. 6, and substantially the same rate characteristic is obtained. For the lithium ion secondary batteries of Example 8 and Comparative Example 7, charging and discharging were repeated in the range of 4.3-3.0V under the conditions of 60 degreeC and the charge-discharge rate of 0.5C. In Fig. 9, the results of the obtained cycle characteristics are shown. 7 , it can be seen that the secondary battery of Example 8 has superior cycle characteristics than the secondary battery of Comparative Example 7.

(iii) Active material: Li _{1 . 2} Mn _{0 . 56} Ni _{0 . 17} Co _{0 . 07} O ₂

Example 9

1.66 g of Li(CH ₃ COO), 2.75 g of Mn(CH ₃ COO) ₂ .4H ₂ O, and 0.85 g of Ni(CH ₃ COO) ₂ .4H ₂ O, and Co(CH ₃ COO) ₂ .4H ₂ 0.35 g of O and 200 mL of distilled water were mixed, the solvent was removed using an evaporator, and the mixture was collected. Next, the collected mixture was introduced into a vibrating ball mill apparatus, and pulverization was performed at 15 hz for 10 minutes to obtain a uniform mixture. The mixture after pulverization is heated in air at 900°C for 1 hour, and lithium excess solid solution Li ₁ having an average particle size of 1 µm or less _{. 2} Mn _{0 . 56} Ni _{0 . 17} Co _{0 . 07} O ₂ crystals were obtained. 91 parts by mass of this crystal grain and 4 parts by mass of the conductive carbon of Example 1 are mixed, and further, 5 parts by mass of polyvinylidene fluoride and an appropriate amount of N-methylpyrrolidone are added and sufficiently kneaded to form a slurry, After apply|coating this slurry on aluminum foil and drying it, the rolling process was performed and the positive electrode for lithium ion secondary batteries was obtained. The electrode density was computed from the measured value of the volume and weight of the active material layer on the aluminum foil in this positive electrode. The value of the electrode density was 3.15 g/cc. Moreover, using the obtained positive electrode, the ethylene carbonate/diethyl carbonate 1: ₁ solution of 1M LiPF6 was used as electrolyte solution, and the lithium ion secondary battery which used lithium as the counter electrode was created. About the obtained battery, the charging/discharging characteristic was evaluated under the conditions of a wide range of current densities.

Comparative Example 8

Li ₁ obtained in Example 9 of 91 parts by mass _{. 2} Mn _{0 . 56} Ni _{0 . 17} Co _{0 . 07} O ₂ particles and 4 parts by mass of acetylene black (primary particle diameter; 40 nm, specific surface area of micropores; 0 m 2 g ^{- 1} ) were mixed, and 5 parts by mass of polyvinylidene fluoride and an appropriate amount of N-methyl After pyrrolidone was added and kneaded enough to form a slurry, this slurry was apply|coated on aluminum foil and dried, the rolling process was performed and the positive electrode for lithium ion secondary batteries was obtained. The electrode density was computed from the measured value of the volume and weight of the active material layer on the aluminum foil in this positive electrode. The value of the electrode density was 2.95 g/cc. Moreover, using the obtained positive electrode, the ethylene carbonate/diethyl carbonate 1:1 solution of ₁ M LiPF6 was used as electrolyte solution, and the lithium ion secondary battery which used lithium as the counter electrode was created. About the obtained battery, the charging/discharging characteristic was evaluated under the conditions of a wide range of current densities.

Fig. 10 is a diagram showing the relationship between the rate and the discharge capacity per volume of the positive electrode active material layer for the lithium ion secondary batteries of Example 9 and Comparative Example 8; As with the result shown in FIG. 6, it turns out that the discharge capacity also increases as the electrode density increases, and substantially the same rate characteristic is obtained. For the lithium ion secondary batteries of Example 9 and Comparative Example 8, charging and discharging were repeated in the range of 4.8 to 2.5 V under conditions of a charge/discharge rate of 25°C and 0.5C. 11 shows the results of the obtained cycle characteristics. 7 , it can be seen that the secondary battery of Example 9 has superior cycle characteristics than the secondary battery of Comparative Example 8 .

(iv) Change of carbon raw material

Example 10

10 g of furnace black having pores (average primary particle diameter of 20 nm, specific surface area of micropores; 1131 m 2 g ^-1 ) was added to 300 mL of 60% nitric acid, and the resulting solution was irradiated with ultrasonic waves for 10 minutes, followed by filtration to obtain furnace black recovered The recovered furnace black was washed with water 3 times and dried to obtain an acid-treated furnace black. 0.5 g of this acid-treated furnace black, 1.98 g of Fe(CH ₃ COO) ₂ , 0.77 g of Li(CH ₃ COO), 1.10 g of C ₆ H ₈ O ₇ .H ₂ O, 1.32 g of CH ₃ COOH , H ₃ PO ₄ 1.31 g and 120 mL of distilled water were mixed, and the resulting mixture was stirred with a stirrer for 1 hour, and then evaporated to dryness at 100° C. in the air to collect the mixture. Next, the obtained mixture was introduced into a vibrating ball mill apparatus, and pulverization was performed at 20 hz for 10 minutes. The pulverized powder was heated in nitrogen at 700° C. for 3 minutes to obtain a composite in which LiFePO ₄ was supported on furnace black.

1 g of the obtained composite was added to 100 mL of an aqueous hydrochloric acid solution having a concentration of 30%, and the obtained solution was irradiated with ultrasonic waves for 15 minutes to dissolve LiFePO ₄ in the composite, and the remaining solid was filtered, washed with water, and dried. A part of the dried solid was heated to 900°C in air by TG analysis, and the weight loss was measured. The process of dissolving LiFePO ₄ with an aqueous hydrochloric acid solution, filtration, washing with water and drying is repeated until it can be confirmed that the weight loss is 100%, that is, LiFePO ₄ does not remain, to obtain LiFePO ₄ free conductive carbon .

Then, 0.1 g of the obtained conductive carbon was added to 20 mL of aqueous ammonia solution of pH11, and ultrasonic irradiation for 1 minute was performed. The obtained liquid was left to stand for 5 hours to precipitate a solid part. After precipitation of the solid part, the residual part from which the supernatant liquid was removed was dried, and the weight of the solid after drying was measured. Weight ratio with respect to the weight 0.1g of the first conductive carbon of the weight which subtracted the weight of the solid after drying from the weight 0.1g of the first conductive carbon was made into content of the "hydrophilic part" in conductive carbon. This conductive carbon contained 13% of hydrophilic part. In addition, the hydrophilic portion in the furnace black having voids used as a raw material is only 2%.

94 parts by mass of commercially available LiNi _{0 . 5} Mn _{0 . 3} Co _{0 . 2} O ₂ particle|grains (average particle diameter of 5 micrometers), 2 mass parts of obtained conductive carbon, and 2 mass parts of acetylene black (primary particle diameter; 40 nm, specific surface area of micropores; 0 m<2>g ^{- 1} ) were mixed. In Fig. 12, a SEM photograph of 50000 times of the obtained mixture is shown. Although the surface of the particle|grains is partially covered with a grass material, and the outline is not grasped clearly, this grass material spreads while conductive carbon obtained by oxidizing a furnace black raw material covers the surface of particle|grains by the pressure of mixing. Moreover, it turns out that fine furnace black with an average primary particle diameter of 20 nm and acetylene black with an average primary particle diameter of 40 nm are disperse|distributing favorably. Although it is generally said that a fine particle is easy to aggregate, the aggregation of a fine particle is effectively suppressed by the conductive carbon obtained by carrying out the oxidation process of the furnace black which has a space|gap.

Next, 2 parts by mass of polyvinylidene fluoride and an appropriate amount of N-methylpyrrolidone are added to the resulting mixture, thoroughly kneaded to form a slurry, and the slurry is coated on an aluminum foil and dried, followed by rolling treatment for lithium A positive electrode for an ion secondary battery was obtained. The electrode density was computed from the measured value of the volume and weight of the active material layer on the aluminum foil in this positive electrode. The value of the electrode density was 3.80 g/cc. Further, using the obtained positive electrode, a lithium ion secondary battery using a 1 M LiPF ₆ ethylene carbonate/diethyl carbonate 1:1 solution as an electrolyte solution and lithium as a counter electrode was prepared. About the obtained battery, the charging/discharging characteristic was evaluated under the conditions of a wide range of current densities. Moreover, charging and discharging were repeated about the obtained battery in the range of 4.6-3.0V under the conditions of 60 degreeC and the charging/discharging rate of 0.5C.

Example 10 and Comparative Example 6 differed in the type of carbon for the positive electrode, but other conditions were the same. In Example 10, conductive carbon and acetylene black obtained from a furnace black raw material having voids were used, but in Comparative Example 6, acetylene Only black was used. The electrode density of the positive electrode in the comparative example 6 was 3.40 g/cc, and the electrode density improved significantly by use of the conductive carbon obtained from the furnace black raw material which has a space|gap. In addition, Example 10 and Example 6 differ in the type of carbon for the positive electrode, but other conditions are the same. In Example 6, conductive carbon and acetylene black obtained from a Ketjen black raw material were used, but in Example 10, furnace black Conductive carbon and acetylene black obtained from raw materials were used. The electrode density of the positive electrode in Example 6 was 3.81 g/cc, and the substantially same electrode density was obtained irrespective of the difference of the raw material in conductive carbon.

13 shows the relationship between the rate and the discharge capacity per volume of the positive electrode active material layer for the lithium ion secondary batteries of Example 10 and Comparative Example 6, and FIG. 14 shows the lithium ion secondary batteries of Example 10 and Comparative Example 6 Shows the results of cycle characteristics for It can be seen from Fig. 13 that as the electrode density increases, the discharge capacity also increases, and substantially the same rate characteristics are obtained. Moreover, when the rate characteristic of the secondary battery of Example 6 in FIG. 6 and the rate characteristic of the secondary battery of Example 10 in FIG. 13 are compared, in the difference of the raw material in the conductive carbon used for a positive electrode Regardless, it can be seen that almost the same rate characteristics are obtained. 14 , it can be seen that the secondary battery of Example 10 has superior cycle characteristics than the secondary battery of Comparative Example 6. Moreover, when the cycling characteristics of the secondary battery of Example 6 in FIG. 7 and the cycling characteristics of the secondary battery of Example 10 in FIG. 14 are compared, in the difference of the raw material in the conductive carbon used for a positive electrode Regardless, it can be seen that almost the same rate characteristics are obtained.

(4) solubility of active material

As mentioned above, the outstanding cycling characteristics of the lithium ion secondary battery provided with the positive electrode which has an active material layer containing the conductive carbon of this invention is substantially the whole of the active material particle surface coat|covered with grass-like carbon, and this glue It is thought that it is because the carbon of a shape suppresses deterioration of an active material, In order to confirm this, the solubility of an active material was investigated.

Each of the conductive carbon and acetylene black of Example 1 was mixed with LiFePO ₄ particles having an average particle diameter of 0.22 μm, LiCoO ₂ particles having an average particle diameter of 0.26 μm, and LiNi _0.5 Mn _0.3 Co _0.2 O ₂ particles having an average particle diameter of 0.32 μm and 5:95 After mixing in a mass ratio, 5 mass % of polyvinylidene fluoride and an appropriate amount of N-methylpyrrolidone of the total are added and thoroughly kneaded to form a slurry, coated on aluminum foil, dried, and rolled to an electrode got A coin-type battery was created using this electrode and the electrolyte obtained by adding 1000 ppm of water to a 1:1 solution of 1 M LiPF ₆ in ethylene carbonate/diethyl carbonate. In this test, microparticles with a large specific surface area were used in order to increase the area of the active material in contact with the electrolyte. In addition, 1000 ppm of water was added for the purpose of an accelerated test, since the active material is easy to melt|dissolve so that there is much water. After leaving this battery at 60 DEG C for one week, it was disassembled, the electrolyte was collected, and the amount of metal dissolved in the electrolyte was analyzed by an ICP emission spectrometer. The results obtained in Table 1 are shown.

As is clear from Table 1, the conductive carbon of Example 1 suppresses the dissolution in the electrolyte of an active material remarkably compared with acetylene black. It is thought that this is because the conductive carbon of Example 1 suppresses aggregation of this microparticle effectively even if it is a microparticle whose active material has an average particle diameter of 0.22-0.32 micrometer, and has coat|covered substantially the whole active material particle surface.

(5) Influence of pressure application to conductive carbon

(i) SEM observation

15 is an SEM photograph of the conductive carbon of Example 1 and the conductive carbon of Comparative Example 4, respectively dispersed in a dispersion medium, the obtained dispersion is applied on an aluminum foil, and a dried coating film is photographed, and a force of 300 kN on the coating film The SEM photograph taken after performing the rolling treatment of is shown. The coating film of the conductive carbon of the comparative example 4 did not show the big change before and behind a rolling process. However, in the coating film of the conductive carbon of Example 1, the surface unevenness|corrugation decreased remarkably by a rolling process so that a SEM photograph might grasp|ascertain, a carbon particle spread, and it became difficult to confirm a grain boundary. Accordingly, it can be seen that the properties of carbon were greatly changed by the strong oxidation treatment.

(ii) Relationship between press pressure and density

For each of the conductive carbon of Example 1 and the conductive carbon (carbon raw material) of Comparative Example 5, the conductive carbon and polyvinylidene fluoride were added to an appropriate amount of N-methylpyrrolidone in a ratio of 70:30 and sufficiently kneaded. After forming a slurry, apply|coating this slurry on aluminum foil and drying, it rolled. Fig. 16 is a view showing the results of investigation of the effect of the press pressure on the carbon density in the rolling process, in which (A) shows the relationship between the press pressure and the density, (B) shows the relationship between the press pressure and the density increase rate, respectively. there is. As is clear from FIG. 16, the conductive carbon of Example 1 has a large density also before a press compared with the conductive carbon of the comparative example 5. In addition, the conductive carbon of Example 1 is greatly affected by the press pressure compared to the conductive carbon of Comparative Example 5, and the density increase rate according to the increase of the press pressure is large, the press pressure is 25 kPa, and the density increase rate exceeds 200%. . Therefore, when a rolling process is performed on the conditions of the same press pressure, it turns out that the conductive carbon of Example 1 is compressed densely compared with the conductive carbon of the comparative example 5. From this, when an electrode is created using the electrode material containing the conductive carbon of Example 1, the conductive carbon of Example 1 is compressed densely by a rolling process, the active material particle approaches each other, and it is that an electrode density improves It is understood.

(iii) Relationship between press pressure and conductivity

For each of the conductive carbon of Example 1 and the conductive carbon (carbon raw material) of Comparative Example 5, the conductive carbon and polytetrafluoroethylene were added to an appropriate amount of N-methylpyrrolidone in a ratio of 70:30, and thoroughly kneaded. It rolled to form a slurry, and after shape|molding this slurry into sheet shape and drying it, the rolling process was performed. Fig. 17 is a view showing the results of investigation of the effect of the press pressure on the carbon conductivity in the rolling process, (A) the relationship between the press pressure and the electrical conductivity, (B) the relationship between the press pressure and the electrical conductivity increase rate, respectively. there is. As is clear from FIG. 17, although the conductive carbon of Example 1 has low electrical conductivity compared with the conductive carbon of Comparative Example 5, since a density increases by a rolling process, it turns out that electrical conductivity also increases with the increase of a press pressure. there is. When an electrode is created using the electrode material containing the conductive carbon of Example 1, the conductive carbon of Example 1 spreads in a pasty shape on the surface of the active material particles by rolling treatment, and the contact area between the conductive carbon and the active material particles increases, but , the conductive carbon spread in the form of grass is densely compressed by contact with the active material particles, and the conductivity of the conductive carbon is improved.

(6) Mixed state of conductive carbon and active material

In order to confirm the mixed state of an active material and carbon, the following experiment was performed.

(i) Mixing of fine particles and carbon

Each of the conductive carbon and acetylene black of Example 1 was introduced into a mortar at a mass ratio of 20:80 with LiNi _0.5 Mn _0.3 Co _0.2 O ₂ microparticles having an average particle diameter of 0.32 µm, followed by dry mixing. 18 shows an SEM photograph at a magnification of 50000 times. When acetylene black is used as carbon, compared with the case where the conductive carbon of Example 1 is used, in spite of being the same mixing conditions, it turns out that the microparticles|fine-particles are aggregated. Therefore, it turns out that the conductive carbon of Example 1 suppresses the aggregation of a microparticle effectively.

(ii) Mixing of coarse particles and carbon

Each of the conductive carbon of Example 1 and acetylene black was introduced into a mortar at a mass ratio of 4:96 with LiNi _0.5 Mn _0.3 Co _0.2 O ₂ coarse particles having an average particle diameter of 5 µm, and dry mixing was performed. 19 shows an SEM photograph at a magnification of 100000 times. When acetylene black is used as carbon, coarse particles and acetylene black exist separately, but when conductive carbon of Example 1 is used, the coarse particles are covered with grass, and the outline of the coarse particles is not clearly grasped. it can be seen that This paste-like material spreads while the conductive carbon of Example 1 covers the surface of a coarse particle by the pressure of mixing. By the rolling treatment at the time of electrode creation, the conductive carbon of Example 1 spreads further in a grassy shape and densifies while covering the surface of the active material particles, so that the active material particles approach each other, and thereby the conductive carbon of Example 1 becomes the active material particles. It is thought that the electrode density increased because the amount of the active material per unit volume in the electrode increased because it was extruded and densely filled in the gap formed between the adjacent active material particles while covering the surface.

<Industrial Applicability>

By use of the conductive carbon of this invention, the electrical storage device which has a high energy density is obtained.

Claims (8)

As conductive carbon used as a conductive agent for an electrode of an electrical storage device,
The conductive carbon includes a hydrophilic portion,
Content of the hydrophilic part is 10 mass % or more of the whole conductive carbon,
It has the property of spreading in the form of grass under pressure,
The grass shape means a state in which the grain boundaries of primary carbon particles are not confirmed and non-particulate amorphous carbon is connected in the SEM photograph taken at a magnification of 25000 times,
The hydrophilic part is obtained by adding 0.1 g of the conductive carbon to 20 ml of an aqueous ammonia solution having a pH of 11, and leaving the solution obtained by performing ultrasonic irradiation for 1 minute for 5 hours to precipitate the solid part, the pH without precipitation It is the part dispersed in the aqueous ammonia solution of 11,
The content of the hydrophilic part is, after precipitation of the solid part, the remaining part from which the supernatant is removed, measuring the weight of the solid after drying, and subtracting the weight of the solid after drying from the weight of the first conductive carbon 0.1g It is obtained by calculating ratio with respect to the weight 0.1g of first conductive carbon, The conductive carbon characterized by the above-mentioned. The method of claim 1,
Conductive carbon whose content of the said hydrophilic part is 12 mass % or more of the whole conductive carbon. As the manufacturing method of the conductive carbon of Claim 1,
A carbon raw material having voids is subjected to oxidation treatment, provided that the oxidation treatment includes a step of performing the oxidation treatment so that the hydrophilic portion in the conductive carbon obtained by the oxidation treatment becomes 10% by mass or more of the total conductive carbon The manufacturing method of conductive carbon characterized by the above-mentioned. A method of manufacturing an electrode material for an electrical storage device, comprising:
The conductive carbon according to claim 1 or 2 and the electrode active material particles are mixed, and by the pressure of mixing, at least a part of the conductive carbon is spread in a pasty shape to cover the surface of the electrode active material particles. Method for producing an electrode material, characterized in that. 5. The method of claim 4,
The average particle diameter of the electrode active material particles is greater than 2㎛ 25㎛, the method for producing an electrode material. 5. The method of claim 4,
The electrode active material particles are fine particles having an average particle diameter of 0.01 to 2 μm that can be operated as a positive electrode active material or a negative electrode active material, and coarse particles having an average particle diameter greater than 2 μm and less than or equal to 25 μm that can be operated as the same electrode active material as the fine particles. A method for producing an electrode material, comprising particles. 5. The method of claim 4,
The manufacturing method of the electrode material which further mixes another conductive carbon with the said conductive carbon and the said electrode active material particle. A method for manufacturing an electrode of an electrical storage device, comprising:
Forming an active material layer on the current collector using the electrode material obtained by the manufacturing method according to claim 4; and
Applying a pressure to the active material layer, and by the applied pressure, the conductive carbon is further spread in a grass shape to cover the surface of the electrode active material particles.

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